DNA tags protect olive oil from false labelling

Researchers in Switzerland have developed an invisible tag to mark the origin of expensive high-quality olive oil, protecting consumers and producers against counterfeiting and adulteration.

The tag consists of tiny magnetic DNA particles encapsulated in a silica casing and mixed with the oil. Just a few grams of the material would be enough to tag the entire olive oil production of Italy.

If counterfeiting were suspected, the particles added at the place of origin could be extracted from the oil and analysed, enabling a definitive identification of the producer. “The method is equivalent to a label that cannot be removed,” said Robert Grass, lecturer in the Department of Chemistry and Applied Biosciences at ETH Zurich.

The researchers wanted to produce a tag that was not only forgery-proof but also invisible, safe, robust, cheap and easy to detect. To meet these criteria they used nanotechnology and a piece of artificial genetic material. “With DNA, there are millions of options that can be used as codes,” Grass explained. Tiny amounts are sufficient for labelling purposes.

However, outside a living organism DNA cannot repair itself, so the researchers used a silica coating to protect it against light, temperature fluctuations and chemical attack. Then they magnetised the tags by attaching iron oxide nanoparticles, so they can be retrieved from the oil quickly and simply.

Experiments in the lab showed that the tiny tags dispersed well in the oil and did not result in any visual changes. They also remained stable when heated and weathered an ageing trial unscathed. The magnetic iron oxide, meanwhile, made it easy to extract the particles from the oil. The DNA was recovered using a fluoride-based solution for PCR (polymerase chain reaction) analysis, which is a standard process for medical laboratories.

“Unbelievably small quantities of particles down to a millionth of a gram per litre and a tiny volume of a thousandth of a litre were enough to carry out the authenticity tests for the oil products,” the researchers wrote in their paper, which has been published in the journal ACS Nano. The method also makes it possible to detect adulteration if the concentration of nanoparticles does not match the original value.

Grass sees great potential for the use of invisible labels in the food industry, where substandard and counterfeit products generate vast profits for criminal gangs. To promote acceptance, natural genetic material could be used in place of synthetic DNA, for instance, from exotic tomatoes or pineapples. Silica particles are already present in ketchup and orange juice, he pointed out, and iron oxide is permitted as a food additive E172.

Petrol could also be tagged using this method and the technology could be used in the cosmetics industry as well. In trials the researchers successfully tagged expensive bergamot essential oil, which is used as a raw material in perfumes.